The present invention relates generally to a system for deploying a parachute during ejection of an occupant from a disabled aircraft, and more particularly to a fail-safe means of sensing airspeed in such a system.
Ejection seats are often provided in high speed, high altitude aircraft for assuring that the occupant will be able to escape from the aircraft in an emergency situation. Once the seat is ejected from the aircraft, the man-seat combination continues along its trajectory in the airstream for a predetermined time after which the recovery parachute is deployed for lowering the occupant safely to the ground. However, due to the widely varying conditions within which the ejection seat system must operate, it is extremely desirable that some means be provided for automatically deploying the parachute at the earliest appropriate time.
There are two basic parameters which generally govern this appropriate time. First, the airspeed existing at the time the parachute is deployed must be within a certain limit, that limit being the one which produces opening forces which does not exceed the structural capabilities of the parachute itself and which is physiologically tolerable for the ejected crewman. Second, deployment must not occur until the ejected crewman is below a certain altitude, that altitude being one at which a human being is capable of surviving for any protracted length of time.
In the typical case, ejection seat systems employ both parameters with inputs of altitude provided by a static port and airspeed provided by a pitot to determine dynamic pressure. Some systems additionally have stabilizing devices and means to separate the occupant safely from the seat.
While these systems are excellent for ejection at reasonably safe altitudes, there is a problem of safe ejection at low altitudes during landing and takeoff and in other such low airspeed/low altitude situations. The foregoing systems will sense the low altitude, but they sometimes will not sense the proper airspeed and, as a result, cause the parachute to open only after a delay.
Various improvements, such as a zero-delay ripcord, have been added to the above systems in order to achieve greater safety in low airspeed/low altitude ejections. However, these improvements are still dependent upon accurate sensing of dynamic pressure through the use of pitots. They will not, for instance, provide for safe ejection during high airspeed/low altitude emergencies when the pitots may be blocked by airborne debris such as canopy fragments.